Field of the Invention
The present invention relates to lead-free low-melting glass compositions. Specifically, the present invention relates to a lead-free low-melting glass composition that is prevented or restrained from crystallization and can thereby soften and flow satisfactorily at a lower temperature. The present invention also relates to a low-temperature sealing glass frit, a low-temperature sealing glass paste, a conductive material, and a conductive glass paste, each of which contains the lead-free low-melting glass composition; and to a glass-sealed component and an electrical/electronic component prepared by using any of them.
Description of Related Art
In some articles, a low-temperature sealing glass frit including a low-melting glass composition and low-thermal-expansion ceramic particles is used typically for sealing and/or bonding. The articles are exemplified by vacuum-insulating double glass panels applied typically to window panes; display panels such as plasma display panels, organic electroluminescent display panels, and fluorescent display tubes; and electrical/electronic components such as quartz resonators, IC ceramic packages, and semiconductor sensors. The low-temperature sealing glass frit is often applied in the form of a low-temperature sealing glass paste. The low-temperature sealing glass paste is applied typically by a screen process printing or dispensing, dried, and fired for use in sealing and/or bonding. Upon the sealing and/or bonding, the low-melting glass composition contained in the low-temperature sealing glass frit or in the corresponding low-temperature sealing glass paste softens, flows, and thereby comes in intimate contact with a member to be sealed and/or to be bonded.
Likewise, a conductive material including a low-melting glass composition and metal particles is used to form an electrode and/or an interconnection in many electrical/electronic components such as solar cells, image display devices, multilayer capacitors, quartz resonators, LEDs (light-emitting diodes), and multilayered circuit boards. The conductive material is also used as a conductive bonding material for conduction. The conductive material is often applied in the form of a conductive glass paste, as with the low-temperature sealing glass frit. The conductive glass paste is applied typically by a screen process printing or dispensing, dried, and fired to form an electrode, an interconnection, and/or a conductive junction. Also upon the formation, the low-melting glass composition contained in the conductive material or in the corresponding conductive glass paste softens, flows, and thereby allows the metal particles to sinter or to be brought into intimate contact with a substrate.
The low-melting glass compositions to be contained in the low-temperature sealing glass frit or the corresponding low-temperature sealing glass paste, as well as the conductive material and the corresponding conductive glass paste have often employed PbO—B2O3 low-melting glass compositions containing a very large amount of lead oxide. The PbO—B2O3 low-melting glass compositions have a low softening point of 350° C. to 400° C., can soften and flow satisfactorily at 400° C. to 450° C., and still have relatively high chemical stability. The “softening point” refers to a second endothermic peak temperature as determined by a differential thermal analysis “DTA”.
However, more safe materials have been demanded in the electrical and electronic equipment industry in accordance with the recent global trend toward green procurement/green design. Typically, the Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment (RoHS directive) took effective on 1 Jul. 2006 by the European Union. The RoHS directive restricts the use of six hazardous materials, i.e., lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ether.
The PbO—B2O3 low-melting glass compositions contain a large amount of lead that is restricted by the RoHS directive and are hardly applied to low-temperature sealing glass frits, corresponding low-temperature sealing glass pastes, conductive materials, and corresponding conductive pastes. Thereby, the development of novel lead-free low-melting glass compositions has proceeded. In addition, strong demands have been made to develop lead-free low-melting glass compositions that soften and flow at a lower temperature as compared with the PbO—B2O3 low-melting glass compositions and still have good chemical stability. These demands have been made so as to allow various glass-sealed components and electrical/electronic components to less undergo thermal damage (to have higher functions) and to have better productivity (with reduced takt time). Specifically, demands have been made to provide lead-free low-melting glass compositions that soften and flow at a temperature of 350° C. or lower, preferably 300° C. or lower, and are applicable typically to sealing and/or bonding or to the formation of electrodes/interconnections and conductive junctions.
Japanese Patent Application Laid-Open No. 2013-32255 (Patent Literature 1) discloses a lead-free low-melting glass composition. The glass composition contains, in terms of oxides, 10 to 60 mass percent of Ag2O, 5 to 65 mass percent of V2O5, and 15 to 50 mass percent of TeO2. The glass composition contains Ag2O, V2O5, and TeO2 in a total content of 75 mass percent to less than 100 mass percent, with the remainder being at least one of P2O5, BaO, K2O, WO3, Fe2O3, MnO2, Sb2O3, and ZnO in a content of greater than 0 mass percent to 25 mass percent. The patent literature mentions that the Ag2O—V2O5—TeO2 lead-free low-melting glass composition has a low softening point of 320° C. or lower, softens and flows at a lower temperature as compared with the conventional PbO—B2O3 low-melting glass compositions, and still has good chemical stability, where the softening point is determined from the second endothermic peak temperature by the differential thermal analysis (DTA). In addition, Patent Literature 1 proposes a low-temperature sealing glass frit, a low-temperature sealing glass paste, a conductive material, and a conductive glass paste each containing the Ag2O—V2O5—TeO2 lead-free low-melting glass composition; and an electrical/electronic component prepared using any of them.